The patch titled Subject: mm: zswap: fix missing folio cleanup in writeback race path has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-zswap-fix-missing-folio-cleanup-in-writeback-race-path.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Yosry Ahmed yosryahmed@google.com Subject: mm: zswap: fix missing folio cleanup in writeback race path Date: Thu, 25 Jan 2024 08:51:27 +0000

In zswap_writeback_entry(), after we get a folio from __read_swap_cache_async(), we grab the tree lock again to check that the swap entry was not invalidated and recycled. If it was, we delete the folio we just added to the swap cache and exit.

However, __read_swap_cache_async() returns the folio locked when it is newly allocated, which is always true for this path, and the folio is ref'd. Make sure to unlock and put the folio before returning.

This was discovered by code inspection, probably because this path handles a race condition that should not happen often, and the bug would not crash the system, it will only strand the folio indefinitely.

Link: https://lkml.kernel.org/r/20240125085127.1327013-1-yosryahmed@google.com Fixes: 04fc7816089c ("mm: fix zswap writeback race condition") Signed-off-by: Yosry Ahmed yosryahmed@google.com Reviewed-by: Chengming Zhou zhouchengming@bytedance.com Acked-by: Johannes Weiner hannes@cmpxchg.org Reviewed-by: Nhat Pham nphamcs@gmail.com Cc: Domenico Cerasuolo cerasuolodomenico@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/zswap.c | 2 ++ 1 file changed, 2 insertions(+)

--- a/mm/zswap.c~mm-zswap-fix-missing-folio-cleanup-in-writeback-race-path +++ a/mm/zswap.c @@ -1442,6 +1442,8 @@ static int zswap_writeback_entry(struct if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) { spin_unlock(&tree->lock); delete_from_swap_cache(folio); + folio_unlock(folio); + folio_put(folio); return -ENOMEM; } spin_unlock(&tree->lock); _

Patches currently in -mm which might be from yosryahmed@google.com are

mm-memcg-optimize-parent-iteration-in-memcg_rstat_updated.patch mm-zswap-fix-missing-folio-cleanup-in-writeback-race-path.patch mm-swap-enforce-updating-inuse_pages-at-the-end-of-swap_range_free.patch mm-zswap-remove-unnecessary-trees-cleanups-in-zswap_swapoff.patch mm-zswap-remove-unused-tree-argument-in-zswap_entry_put.patch x86-mm-delete-unused-cpu-argument-to-leave_mm.patch x86-mm-clarify-prev-usage-in-switch_mm_irqs_off.patch